In the display technology, an OLED (Organic Light Emitting Diode) display is generally recognized as a third-generation display technology after a LCD (Liquid Crystal Display) by the industry because of its advantages of slim, active light emission, high response speed, wide viewing angle, rich colors, high brightness, low power consumption, high and low temperature resistance and the like.
At present, the OLED display mainly adopts current control type light emission, and the uniformity of light emission is controlled by corresponding current. However, since the threshold voltage of driving transistors of each pixel of the OLED display easily drifts with time, the current flowing through an OLED deviates under a same data signal, causing non-uniform display brightness.
The problem of mura caused by unobscured dark states of the OLED light emitting elements and insufficient compensation for the threshold voltage of the driving transistors still exist when a pixel circuit is optimized with existing techniques an actual product. The existing techniques offer a number of solutions to improve the unobscured dark states and the insufficient compensation for the threshold voltage of the driving transistors. For example, in an application for a patent published as CN106097964A, a pixel circuit and a driving method are proposed, and the pixel circuit can compensate the threshold voltage, and reduce leakage current so as to ensure high contrast in the dark state (the unobscured dark state). However, the technical solution also has the disadvantages of having complex layout designs and involving a large number of transistors and signal leads. Therefore, it is urgent to find a technical solution which not only solves the problems of the unobscured dark states and the insufficient compensation for the threshold voltage of the driving transistors effectively, but also eliminates the complexity in layout designs.